Laminated glass

Laminated glass is a type of safety glass that holds together when shattered. In the event of breaking, it is held in place by an interlayer, typically of polyvinyl butyral (PVB) or ethylene-vinyl acetate (EVA), between its two or more layers of glass. The interlayer keeps the layers of glass bonded even when broken, and its high strength prevents the glass from breaking up into large sharp pieces. This produces a characteristic 'spider web' cracking pattern when the impact is not enough to completely pierce the glass. In the case of the EVA, the thermoset EVA, offers a complete bounding (cross-linking) with the material whether it is glass, polycarbonate, PET, or other types of products. Laminated glass is a type of safety glass that holds together when shattered. In the event of breaking, it is held in place by an interlayer, typically of polyvinyl butyral (PVB) or ethylene-vinyl acetate (EVA), between its two or more layers of glass. The interlayer keeps the layers of glass bonded even when broken, and its high strength prevents the glass from breaking up into large sharp pieces. This produces a characteristic 'spider web' cracking pattern when the impact is not enough to completely pierce the glass. In the case of the EVA, the thermoset EVA, offers a complete bounding (cross-linking) with the material whether it is glass, polycarbonate, PET, or other types of products. Laminated glass is normally used when there is a possibility of human impact or where the glass could fall if shattered and also for architectural applications. Skylight glazing and automobile windshields typically use laminated glass. In geographical areas requiring hurricane-resistant construction, laminated glass is often used in exterior storefronts, curtain walls and windows. Laminated glass is also used to increase the sound insulation rating of a window, where it significantly improves sound attenuation compared to monolithic glass panes of the same thickness. For this purpose a special 'acoustic PVB' compound is used for the interlayer. In the case of the EVA material, no additional acoustic material is required, since the EVA provides sound insulation. An additional property of laminated glass for windows is that a PVB and EVA interlayer can block essentially most ultraviolet radiation. A thermoset EVA could block up to 99.9% of all UV rays. In 1902, the French Le Carbone corporation obtained a patent for coating glass objects with celluloid in order to render them less susceptible to cracking or breaking. Laminated glass was invented in 1903 by the French chemist Édouard Bénédictus (1878-1930), inspired by a laboratory accident. A glass flask had become coated with the plastic cellulose nitrate and when dropped shattered but did not break into pieces. However, it was not until 1909 that Benedictus filed a patent, after hearing about a car accident where two women were severely injured by glass debris. In 1911, he formed the Société du Verre Triplex, which fabricated a glass-plastic composite to reduce injuries in car accidents.. Production of Triplex glass was slow and painstaking, making it expensive. It was not immediately widely adopted by automobile manufacturers, but laminated glass was widely used in the eyepieces of gas masks during World War I. In 1912, the process was licensed to The English Triplex Safety Glass Company. Subsequently, in the United States, both Libbey Owens-Ford and Du Pont de Nemours with Pittsburg Plate Glass produced Triplex. Meanwhile, in 1905, John Crewe Wood, a solicitor in Swindon, Wiltshire, England, patented a laminated glass for use as windscreens / windshields. The layers of glass were bonded together by Canada balsam. In 1906 he founded the Safety Motor Screen Co. to produce and sell his product. In 1927, the Canadian chemists Howard W. Matheson and Frederick W. Skirrow invented the plastic polyvinyl butyral (PVB). By 1936, United States companies had discovered that laminated 'safety glass' consisting of a layer of polyvinyl butyral between two layers of glass would not discolor and was not easily penetrated during accidents. Within five years, the new safety glass had virtually replaced its predecessor. In the Road Traffic Act of 1930, the British parliament required new cars to use windscreens of 'safety glass'. By 1939, some 600,000 square feet (56,000 m2) of 'Indestructo' safety glass was being used every year in vehicles produced at the Ford Motor Company works in Dagenham, England. 'Indestructo' safety glass was manufactured by British Indestructo Glass, Ltd. of London. This was the laminated glass used by the Ford Motor Company in 1939, chosen because 'it gives the most complete protection. In addition to being splinter-proof, it is crystal clear and permanently non-discolourable.' This quote hints at some of the technical issues, problems and concerns that stopped laminated glass from being widely used in automobiles immediately after it was invented.